There's not really a simple way to describe notion. It's just a really simple way to organize information.
I've used notion most of my adult life to organize ideas, content, lists, and anything else that my brain has trouble holding on to.
I recommend it more as a personal organizational tool than anything else, and they have an unlimited free plan that serves that purpose beautifully.
I've seen a ton of different startups use it to share and organize documents and send them to clients or contractors to make sure everyone's on the same page.
But what I most respect notion for is the UI that they have created . I've seen so many other tools, especially workspace tools, copy the UI that they designed just because they couldn't come up with anything better.
It's unreasonably smooth, and unreasonably easy to use, And it's free for personal use. That's why I like it so much.
They've got a lot of additional tools that you may also be interested in, like publishing documents as indeendent websites, and an AI assistant inside of your document system. But I just love them for their interface.